U.S. patent application number 12/384510 was filed with the patent office on 2010-04-29 for optical structure and solar cell using the same.
Invention is credited to Jain-Cheng Chen, Shih-Chi Chien, Tim Hsiao, Chen-Hsiang Hsu, Hsiung-Yu Tsai, Chung-Ying Wu, Wen-Chun Yeh.
Application Number | 20100101640 12/384510 |
Document ID | / |
Family ID | 41228018 |
Filed Date | 2010-04-29 |
United States Patent
Application |
20100101640 |
Kind Code |
A1 |
Chen; Jain-Cheng ; et
al. |
April 29, 2010 |
Optical structure and solar cell using the same
Abstract
An optical structure is characterized by improving a primary
lens of a photovoltaic concentrator system. The optical structure
is accomplished by properly dividing the primary lens, determining
required optical operational regions, and arranging the optical
operational regions basing on an identical location into an annular
array, thereby forming the complete optical structure. The optical
structure facilitates enhancing uniformity of light distribution
throughout the optical operational regions, improving photoelectric
conversion efficiency of a solar cell having the optical structure,
and reducing operational distance between the primary lens and the
solar cell.
Inventors: |
Chen; Jain-Cheng; (Kaohsiung
County, TW) ; Wu; Chung-Ying; (Tainan County, TW)
; Tsai; Hsiung-Yu; (Zhubei City, TW) ; Yeh;
Wen-Chun; (Taoyuan County, TW) ; Hsu;
Chen-Hsiang; (Taoyuan County, TW) ; Hsiao; Tim;
(Taoyuan County, TW) ; Chien; Shih-Chi; (Taipei
City, TW) |
Correspondence
Address: |
Raymond Sun
12420 Woodhall Way
Tustin
CA
92782
US
|
Family ID: |
41228018 |
Appl. No.: |
12/384510 |
Filed: |
April 6, 2009 |
Current U.S.
Class: |
136/256 ;
250/214R; 250/216; 359/619 |
Current CPC
Class: |
Y02E 10/52 20130101;
H01L 31/0543 20141201; F24S 23/31 20180501; G02B 3/08 20130101 |
Class at
Publication: |
136/256 ;
250/214.R; 250/216; 359/619 |
International
Class: |
H01L 31/0236 20060101
H01L031/0236; H01L 31/0232 20060101 H01L031/0232; H01L 31/04
20060101 H01L031/04; G02B 27/12 20060101 G02B027/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2008 |
TW |
097206049 |
Claims
1. An optical structure, comprising a plurality of identical
optical operational regions, wherein the optical operational
regions based at an identical location are linked up in an annular
array, the identical optical operational regions being formed by
dividing a semi-finished optical structure upon divisional
benchmarks that are determined by classifying wavelengths of light
rays entering the semi-finished optical structure.
2. The optical structure of claim 1, wherein each of the optical
operational regions comprises a central circle, and a plurality of
refraction portions of concentric arc-shape relative to the central
circle are arranged in a progressive order, the optical operational
regions being arranged in the annular array relative to a center
composed of the central circles on tips of the optical operational
regions, thereby generating multiple focal points.
3. The optical structure of claim 2, wherein the refraction
portions are tooth-shaped in a sectional view and are arranged in a
pattern of concentric arcs relative to the central circle of the
optical operational region.
4. An optical structure, comprising a rough side whereon a
plurality of central circles arranged in an annular array and a
plurality of refraction portions of concentric arc-shape provided
and arranged in a progressive order are centrally carved, wherein
each of the central circles and the refraction portions concentric
to the central circle compose an optical operational region, so
that the optical operational regions cast light rays onto a
photoelectric conversion module and in turn generate multiple focal
points.
5. The optical structure of claim 4, wherein the refraction
portions are tooth-shaped in a sectional view and are arranged in a
pattern of concentric arcs relative to the central circle of the
optical operational region.
6. The optical structure of claim 4, wherein the photoelectric
conversion module further comprises: a frame mounted thereon with
the optical structure; a substrate including a circuit, provided
below the frame, and mounted thereon with a semiconductor chip
facing and corresponding in position to the optical structure; and
a cell electrically connected with the substrate; wherein the
optical structure concentrates the light rays on the semiconductor
chip and converts energy of the light rays into electric power and
then saves the electric power in the cell connected with the
substrate for being later supplied to other powered devices.
7. The optical structure of claim 6, wherein the semiconductor chip
is a .quadrature.-V semiconductor chip.
8. The optical structure of claim 6, wherein the cell is one of a
rechargeable lithium cell and a Ni-MH cell.
9. A solar cell using an optical structure, the solar cell
comprising: at least one said optical structure comprising a rough
side whereon a plurality of central circles arranged in an annular
array and a plurality of refraction portions concentric to the
central circles and arranged in a progressive order are centrally
carved; and a photoelectric conversion module facing and
corresponding in position to the optical structure and converting
energy of light rays concentrated by the optical structure into
electric power; wherein each of the central circles and the
refraction portions concentric to the central circle define an
optical operational region, so that the optical operational regions
cast the light rays onto a photoelectric conversion module and in
turn generate multiple focal points.
10. The solar cell of claim 9, wherein the photoelectric conversion
module further comprises: a frame mounted thereon with the optical
structure; a substrate including a circuit, provided below the
frame, and mounted thereon with a semiconductor chip facing and
corresponding in position to the optical structure; and a cell
electrically connected with the substrate; wherein the optical
structure concentrates the light rays on the semiconductor chip and
converts energy of the light rays into electric power and then
saves the electric power in the cell connected with the substrate
for being later supplied to other powered devices.
11. The solar cell of claim 9, wherein the refraction portions are
tooth-shaped in a sectional view and are arranged in a pattern of
concentric arcs relative to the central circle of the optical
operational region.
12. The solar cell of claim 10, wherein the semiconductor chip is a
.quadrature.-V semiconductor chip.
13. The solar cell of claim 10, wherein the cell is one of a
rechargeable lithium cell and a Ni-MH cell.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention The present invention relates to
an optical structure applicable to a concentrator system in a solar
cell.
[0002] 2. Description of the Prior Art
[0003] In recent years, due to increasing energy costs and global
warming issues, requests for renewable energy bringing less
contamination have attracted extensive attention. Especially, solar
photovoltaic systems relying on the unfailing solar energy have
been developed with various materials and techniques in a worldwide
scale for pursuing maximized photoelectric conversion efficiency
and reduced power generation costs. Typically, a photovoltaic
concentrator system comprises a condensing lens and a
high-efficiency solar cell, thereby providing excellent
power-generation efficiency with reduced costs of land use per unit
area. Besides, such solar photovoltaic systems are not only
superior to the traditional thermal power generation solutions in
economy but also free from concerns related to waste gas and noise,
thus having potential of market growth.
[0004] Conventionally, a Fresnel lens is implemented to
substantially focus sunlight on the center of a solar cell. Though
the Fresnel lens facilitates photocurrent generation, it
nevertheless causes uneven current distribution that results in
significant loss of heat from resistors and high operating
temperature thereof, thus bringing about deteriorating efficiency
of the solar cell. In addition to improving thermal dissipation,
another approach to enhancing the photoelectric conversion
efficiency in a solar cell is to use a Fresnel lens to provide
better uniformity of light concentration.
[0005] Please refer to FIG. 1 for a primary lens 2 of a typical
photovoltaic concentrator system. Therein, a Fresnel lens or a
mirror is provided to gather sunlight rays 1 into a concentration
region 3. Optical properties of light vary with wavelengths of
light. Hence, variation in the extent of concentration increases
markedly when light of a wide range of wavelengths enters the
primary lens 2.
[0006] For instance, there is a great difference in the refractive
index of the same plastic material between a light ray with a long
wavelength and a light ray with a short wavelength. Under non-total
reflection, if light rays with different wavelengths fall on the
same optical material at the same incidence angle, the light rays
leave the optical material at different emergence angles, depending
on wavelength. This can be easily proven by putting an observation
plane behind the optical material.
[0007] When applied to collection of light with multiple
wavelengths, a solar cell using the traditional primary lens
becomes inefficient, because the photoelectric conversion
efficiency of the solar cell is highly associated with the range of
concentration of light energy involving specific wavelengths of
light. Particularly, assuming that different light wavelengths are
associated with different concentration ranges, to collect light
energy to the full from light rays of all effective wavelengths, a
solar cell must has its concentration region made large enough to
meet the light wavelength that requires the largest concentration
range. However, most of collectable light rays are only available
to part of the solar cell, causing inefficient utilization of the
solar cell.
[0008] Please refer to FIG. 2A for a top view of a conventional
primary lens 2 that has been designed and cut into a square. FIG.
2B is a partially enlarged view of the primary lens 2 shown in FIG.
2A. FIG. 2C is a polar diagram derived in a conventional
illumination test where a light source with a short wavelength at
546.1 nm passes through the conventional primary lens 2. FIG. 2D is
a polar diagram showing a light source with a long wavelength at
1300 nm passing through the conventional primary lens 2. Through
FIGS. 2C and 2D, it is learned that light rays with different
wavelengths cause different concentration ranges.
SUMMARY OF INVENTION
[0009] An objective of the present invention is to provide an
optical structure that comprises a plurality of optical operational
regions linked up in an annular array and based at the same
location so as to increase focal points.
[0010] Another objective of the present invention is to provide an
optical structure that implements a plurality of focal points to
distribute light over a photoelectric conversion module so as to
maintain a solar cell using the optical structure at a relatively
low operating temperature and improve photoelectric conversion
efficiency of the solar cell.
[0011] The previously mentioned conventional photovoltaic
concentrator system needs a conventional primary lens for
collecting sunlight. However, the conventional primary lens fails
to accurately concentrate light rays of different wavelengths in
the same area but presents a variable concentration region in
answering to the light rays with different wavelengths. Hence, the
present invention is aimed at improving the conventional primary
lens for a solar photovoltaic system so as to enable the improved
optical structure to concentrate light rays with different
wavelengths in a certain operational region. Besides, the present
invention equalizes concentration areas of light rays with
different wavelengths so as to allow full use of the light rays,
thereby enhancing light uniformity and luminance, and significantly
improving efficiency of the solar cell. The optical structure of
the present invention can be easily applied to the conventional
primary lens and thus is economically beneficial.
[0012] According to a known principle of optics, the smaller the
included angle between the direction in which light rays with
different wavelengths travel and the normal vector of a solar cell,
the closer the locations where the light rays enter the solar cell.
Given the aforementioned principle, the present invention
appropriately divides an existing primary lens as needed, so as to
limit boundaries of concentration areas of light rays with
different wavelengths to a certain range. Thus, when ranges
required by plural identical primary optical operational regions
are all limited, light rays with different wavelengths can be
collected in a limited range. From another respect, the present
invention features limiting light rays in a certain area where the
light rays overlap, thereby improving photoelectric conversion
efficiency of the solar cell reasonably.
[0013] In view of this, the present invention involves
appropriately dividing a primary lens and determining required
optical operational regions. Therein, a plurality of said optical
operational regions are linked up in an annular array based at the
same location so as to construct a complete optical structure. By
the improved optical structure, the present invention facilitates
improving uniformity throughout the operational regions and
increasing the number of focal points, thereby lowering operating
temperature, improving photoelectric conversion efficiency,
maximizing the service life of the solar cell, and reducing the
operational distance between the primary lens and the solar
cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention as well as a preferred mode of use, further
objectives and advantages thereof will be best understood by
reference to the following detailed description of an illustrative
embodiment when read in conjunction with the accompanying drawings,
wherein:
[0015] FIG. 1 is a schematic drawing showing light paths of a
conventional primary lens;
[0016] FIG. 2A is a top view the conventional primary lens;
[0017] FIG. 2B is a partially enlarged view of the conventional
primary lenses;
[0018] FIG. 2C is a polar diagram showing a light source with a
wavelength at 546.1 nm passing through the conventional primary
lens and presented in a concentration region;
[0019] FIG. 2D is a polar diagram showing a light source with a
wavelength at 1300 nm passing through the conventional primary lens
and presented in a concentration region;
[0020] FIG. 3A is a schematic drawing showing divisional lines on a
primary lens according to the present invention;
[0021] FIG. 3B is a schematic drawing showing four optical
operational regions after division jointly forming a complete
optical structure of the present invention;
[0022] FIG. 3C is a partially enlarged vie of the optical structure
of the present invention;
[0023] FIG. 3D is a polar diagram showing a light source with a
wavelength at 546.1 nm passing through the optical structure of the
present invention and presented in a concentration region;
[0024] FIG. 3E is a polar diagram showing a light source with a
wavelength at 1300 nm passing through the optical structure of the
present invention and presented in a concentration region;
[0025] FIG. 4 is a sectional view of the optical structure of the
present invention;
[0026] FIG. 5 is a schematic drawing describing a solar cell using
the optical structure of the present invention; and
[0027] FIGS. 6A and 6B are maps of energy distribution measured and
plotted against different distances between the disclosed optical
structure and a semiconductor chip in the solar cell.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] The present invention is characterized by dividing a typical
primary lens 2 into several optical operational regions. To define
each said optical operational region, divisional benchmarks are
determined taking similar light-entering ranges of light
wavelengths. Besides, a divisional angle is determined according to
a shape of a concentration region, wherein the angle is derived
from dividing 360 degrees by N, where N denotes the number of sides
of the polygonal concentration region. Furthermore, the area of the
intended concentration region is controlled by a distance between
the concentration region and the benchmarks. Afterward, a tip of
the optical operational region is taken as a center of rotation so
as to form an annular array filling the 360-degree area. Hence, N-1
said regions are integrated into a whole optical structure, thereby
accomplishing the present invention.
[0029] Please refer to FIG. 3A. Therein, a triangular optical
operational region 5 is defined on a typical rectangular primary
lens 2 along divisional lines 4 adjacent to benchmarks. The optical
operational region 5 includes a rough side 52. At the rough side
52, a central circle 521 is located at a tip of the optical
operational region 5, and a plurality of refraction portions 522 of
concentric arc-shape are arranged on the circumference of the
central circle 521.
[0030] Referring to FIGS. 3B and 3C, according to the present
embodiment, four identical said optical operational regions 5 are
arranged in an annular array such that the optical operational
regions 5 encircle a center comprising the central circles 521 on
the tips thereof, thereby forming an optical structure 6 shaped as
a complete square. Boundaries between adjacent said optical
operational regions 5 may be realized by any proper connection
approach. Of course, the number of the optical operational regions
5 is not to be limited by the present embodiment. Instead, the
primary lens 2 may be divided into any number of the optical
operational regions 5 as needed.
[0031] FIG. 3D is a polar diagram derived from a illumination test
where a light source with a wavelength at 546.1 nm passes through
the optical structure 6 of the present invention. As compared with
FIG. 2C derived under identical testing conditions, it is learned
that the light with the same wavelength presents an evener and more
concentrated luminance when passing through the optical structure 6
of the present invention than when passing through the conventional
primary lens 2.
[0032] FIG. 3E is a polar diagram derived from a illumination test
where a light source with a wavelength at 1300 nm passes through
the optical structure 6 of the present invention. As compared with
FIG. 2D derived under identical testing conditions, it is learned
that the light with the same wavelength presents an evener and more
concentrated luminance when passing through the optical structure 6
of the present invention than when passing through the conventional
primary lens 2. As a whole, the optical structure 6 of the present
invention has a compact concentration region with improved
concentration uniformity while significantly increasing luminous
flux per unit area, thereby improving the photoelectric conversion
efficiency of a solar cell using the optical structure 6.
[0033] Referring to FIG. 4, the optical structure 6 of the present
invention may be an integrally formed multi-focal Fresnel lens. The
optical structure 6 comprises a smooth side 61 and a rough side 62.
Carved at the center of the rough side 62 are a plurality of
central circles 621 arranged in an annular array and a plurality of
refraction portions 622 of concentric arc-shape relative to the
central circles 621 and arranged in a progressive order. These
refraction portions 622 are tooth-shaped in a sectional view of the
optical structure 6 as shown in FIG. 4. The central circles 621 and
refraction portions 622 are configured under consideration of light
interference and light diffraction and according to required
relative sensitivity and reception angle so that light passing
therethrough is cast onto a photoelectric conversion module 7 (as
shown in FIG. 5), and in consequence multiple focal points
positioned differently are provided on the photoelectric conversion
module 7.
[0034] The optical structure 6 is a square transparent plate with
the smooth side 61 serving to receive sunlight and the rough side
62 serving to concentrate light rays passing therethrough. Of
course, it is feasible that the rough side 62 serves to receive and
concentrate sunlight for the smooth side 61 to further cast out the
concentrated light rays. Alternatively, the optical structure 6 may
be the one shown in FIG. 3A where plural identical said optical
operational regions 5 are arranged in an annular array relative to
a center composed of the central circles 521 on their tips, thereby
forming an optical structure 6 shaped as a complete square.
[0035] Referring to FIG. 5, a solar cell 10 using the optical
structure 6 of the present invention comprises at least one said
optical structure 6 and the photoelectric conversion module 7. The
photoelectric conversion module 7 further comprises a frame 71, a
substrate 72, and a cell 73. The optical structure 6 is mounted
atop the frame 71. The substrate 72 includes a circuit and is
provided below the frame 71 to electrically connect with the cell
73. Beside, a semiconductor chip 721 is mounted on the substrate 72
to face the optical structure 6.
[0036] The optical structure 6 may comprise four or more said
optical operational regions 5 arranged in an annular array relative
to a center composed of the central circles 521 on their tips. Then
the optical structure 6 is mounted atop the frame 71 of the
photoelectric conversion module 7 and facing the substrate 72 with
a predetermined distance H therebetween, wherein the predetermined
distance H determines the focal range where the optical structure 6
casts light on the semiconductor chip 721.
[0037] When light rays enter the optical structure 6, a focal point
generated by the central circles 521 and the refraction portions
522 concentric to the central circles 521 of the optical
operational regions 5 is cast on to the substrate 72 so that the
light rays are collected on the semiconductor chip 721 of the
substrate 72 for photoelectric conversion. Afterward, the resultant
electric power is stored in the cell 73 connected with the
substrate 72 for being supplied to other powered devices. In the
solar cell 10 using the optical structure 6 of the present
invention, the semiconductor chip 721 may be a III-V semiconductor
chip and the cell 73 may be one of a rechargeable lithium cell and
a Ni-MH cell.
[0038] In the solar cell 10 using the optical structure 6 of the
present invention, the solar cell 10 composed of the semiconductor
chip 721, namely the III-V semiconductor chip (GaAs, InP, InGaP),
has excellent photoelectric conversion efficiency, about
26%.about.28%. When made into a multijunctiontandem cell
(InGaP/GaAs//InGaAs), the photoelectric conversion efficiency can
be increased to about 33.3%. Therefore, the solar cell 10 according
to the present invention benefits by the reliability and stability
contributed by the III-V semiconductor chip 721, thus having less
tendency to aging and deterioration even working outdoor and being
less sensitive to temperature variation.
[0039] The characteristic of photovoltaic concentrator has close
relationship with the light concentrating factor (C) and resistance
(Rs), which can be represented by the following mathematic
formulas:
Current: I.sub.L=CI.sub.L,1;
Voltage: V.sub.OC,C=V.sub.OC,1+(nkT/e)InC;
Power:
P=CP.sub.1+CI.sub.L,1.DELTA.V.sub.OC,C-C.sup.2I.sub.L,1.sup.2Rs;
[0040] Wherein, I.sub.L,1 is the current before the light is
concentrated; V.sub.OC,1 is the voltage before the light is
concentrated; k is the Boltzmann constant value; T is the absolute
temperature.
[0041] In the other hand, by improving the uniformity of the light
focused on the semiconductor chip 721, the dark current can also be
reduced, the conversion efficiency can be increased, and the
operating temperature of the photoelectric conversion module 7 can
also be improved. The conversion efficiency of the semiconductor
chip 721 of photoelectric conversion module 7 and the temperature
have the following mathematic relationship:
[0042] Short-Circuit Current: the relationship between I.sub.SC and
temperature is:
I SC = I L - AT r [ exp ( qV - Eg nkT ) ] ; ##EQU00001##
[0043] Wherein, T is the temperature; Eg is the energy gap of
semiconductor.
[0044] Open-Circuit Voltage: the relationship between
V.sub.OC.quadrature.I.sub.SC is:
V OC .apprxeq. ( nkT e ) ln ( J SC J o ) . ##EQU00002##
[0045] Taking the solar cell 10 composed of the III-V semiconductor
chip 721 as example, the photoelectric conversion efficiency
thereof decreases by about 0.067% when the temperature increases by
about 1.degree. C. Thus, the multi-focal optical structure 6 also
facilitates maintaining the optimal temperature for the
semiconductor chip 721 by effectively lowering the peak temperature
of the semiconductor chip 721 during light concentration.
[0046] In the present embodiment, the optical structure 6 may have
four optical operational regions 5 as shown in FIG. 3B so as to
generate four different focal points at the same time when passed
by light rays and evenly distribute the four focal points over the
semiconductor chip 721 (III-V semiconductor chip), thereby
maintaining the semiconductor chip 721 at a relatively low
temperature and thus ensuring the photoelectric conversion
efficiency. In other words, the photoelectric conversion efficiency
of the semiconductor chip 721 is ensured from being adversely
affected by the excessive temperature happening in a single-focal
optical structure.
[0047] Similarly, with quantitative increase of the optical
operational regions 5 of the optical structure 6, the focal points
generated by the optical operational regions 5 on the semiconductor
chip 721 increase in a proportional manner while being evenly
distributed over the semiconductor chip 721. Of course, a plurality
of said optical structures 6 may be provided on the frame 71 of the
photoelectric conversion module 7 to face and correspond to a
plurality of said semiconductor chips 721 on the substrate 72 so as
to further enhance the photoelectric conversion efficiency of the
solar cell 10, thus achieving prompt charging the cell 73.
[0048] Reading FIGS. 6A and 6B with reference to FIG. 5,
distribution of energy of light is measured and plotted against
different distances between the disclosed optical structure 6 and
the semiconductor chip 721.
[0049] As shown in FIG. 6A, when the distance H between the optical
structure 6 of the solar cell 10 and the semiconductor chip 721 is
relatively small, the four focal points draw light rays pass
therethrough close to the center of the semiconductor chip 721. At
this time, since the four focal points are partially overlapped due
to the relatively small distance, the light rays are collected on
the semiconductor chip 721 with enhanced uniformity and
concentration while thermal energy generated by the concentrated
light rays is evenly distributed over the semiconductor chip 721,
but not rivet on the center of the semiconductor chip 721.
[0050] As can be seen in FIG. 6B, when the distance H between the
optical structure 6 of the solar cell 10 and the semiconductor chip
721 is relatively large, the four focal points evenly distribute
light rays passing therethrough to four corners of the
semiconductor chip 721. At this time, owing to the increased
distance, the focal range is enlarged and the multiple focal points
evenly distribute thermal energy generated by the concentrated
light rays over the semiconductor chip 721, thereby maintaining the
semiconductor chip 721 relatively cool and ensuring the
photoelectric conversion efficiency.
[0051] However, it is to be noted that the distance H between the
optical structure 6 and the semiconductor chip 721 is associated
with the area of the optical structure 6 that receives
illumination. In other words, the larger the area of the optical
structure 6 receiving light is, the longer the focal length between
the optical structure 6 and the semiconductor chip 721 is,
rendering the larger distance between the optical structure 6 and
the semiconductor chip 721.
[0052] On the contrary, the smaller the area of the optical
structure 6 receiving illumination is, the shorter the focal length
between the optical structure 6 and the semiconductor chip 721 is,
rendering the smaller distance between the optical structure 6 and
the semiconductor chip 721. Similarly, when the optical structure 6
with a fixed area of illumination works with photoelectric
conversion modules 7 in different sizes, variable focal lengths
would be achievable, so as to provide the optimal focal efficiency
at the semiconductor chip 721 on the substrate 72.
[0053] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *